Windows runs pretty smoothly on a Chromebook.
At least it does for Redditor Coolstar. He's managed to port Windows 8.1 successfully on to his Acer C720 Chromebook, a cheap laptop with 4 GB of RAM and an Intel Celeron processor. Keyboard, graphics, audio, Wi-Fi, and USB are all working.
As you can see from the video below, games like Asphalt 8 play smoothly.
Not all the drivers and features are working yet, such as brightness control, touchscreen support, and, notably, the trackpad. Also, there's no assurance that this will work on all Chromebook models and you'll probably need a Chromebook with at least 64 GB or higher to get this to work.
However, it is a promising project. If you'd like to hack your Chromebook yourself, keep an eye on this Reddit thread or Coolstar's status page, since he says he'll be releasing the drivers once he gets more working.
[h/t OMG! Chrome]